heater trouble

[Rollie396]

I'm having trouble with the heater in my 80 (no ac).A bit of history first.The heater has always blown super hot since I got it.The only issue I had is the hot/cold lever didn't function,so it was either full bore or nothing.
I went on a 3hr roadtrip the other day and it was cool outside (-25c) but the heater put out great.I had it on with the fan on low and the window cracked 1/2".It was comfortable.When I got to the farm I pulled the truck in and did a bit of maintenance.I retorqued the heads which were pretty good,the outside row took a few pounds but nothing serious.I played with choke on the 1406 a bit more (a thread on it's own ),and then I decided to fix the hot/cold lever.
Turned out that a po discoed the cable and tied the door in the full hot position.I hooked the cable up again and tested it,everything seemed fine so I buttoned it up,gave myself an attaboy and moved on.
So today I head for home and it's about the same temp as the day I drove up that way.I noticed the heat wasn't anywhere near as hot as before and it seemed to get cooler the faster I drove and the longer I was on the road.To add to that I noticed the water temp rising a little,so I figured I was running low on coolant somehow.I pulled over,shut the truck down and started checking hoses.The lower rad hose was warmish,both heater hoses warm/hot and upper rad hose hot.I carefully removed the rad cap to check the level and lost a bit doing so but it wasn't much.I topped it up and refired the truck with the cap off.The level dropped immediately so I added another 1/2gallon or so to top it up and put the cap back on.Just for my own piece of mind,I checked the oil it was clean and at the proper level,so I continued on.The engine ran at normal temp the rest of the way,but still no real heat.The only thing that really changed here was I "fixed" the hot cold flapper.What could I have messed up in doing so?
Sorry for the novel.Thanks for any help.